Optical sub-assemblies (OSA) used in optic-electronic transmission may be divided into two types depending on the functional element assembled thereto, namely, transmitter optical sub-assemblies (TOSA) and receiver optical sub-assemblies (ROSA). TOSA is a functional element-to-fiber device and includes a functional element, which may be, for example, a semiconductor laser or a light emitting diode, so that an electrical signal may be converted into light that is coupled into the optical fiber via a lens and then transmitted via the optical fiber. On the other hand, ROSA is a fiber-to-detector device to convert light transmitted via the optical fiber into an electrical signal. The TOSA and the ROSA may be combined into a bi-directional or duplex transceiver OSA.
Up to date, there have been developed a variety of methods for manufacturing OSA. Among others, injection molding using transparent thermoplastic material is low-cost and becomes a main stream for manufacturing the OSA. U.S. Pat. No. 5,631,991, U.S. Pat. No. 6,432,733 B1, and U.S. Pat. No. 6,302,596 B1 (as shown in FIG. 1) are some examples of OSA made through injection molding using thermoplastic material. However, the OSA, such as the one shown in FIG. 1, which is made in the above-mentioned method, usually has the following problems during the manufacturing process:                1. Please refer to FIG. 1 in which an OSA A1 having an integrally injection-molded axially extended one-piece housing A2 is shown. The housing A2 is provided at a first end with a first aperture (fiber receptacle) A3 for an optical fiber 20 to assemble thereto, and at a second end opposite to the first end with a second aperture (LD barrel) A4 for a functional element 30 to assemble thereto. A lens A5 is provided on the housing between the first and the second aperture A3, A4. The lens A5 may be integrally formed on the housing A2, as shown in FIG. 1, or separately formed as that disclosed in U.S. Pat. No. 5,631,991 or U.S. Pat. No. 6,432,733 B1. Since it is highly difficult to make the mold for forming the housing A2, it is uneasy to control the quality of an injection-molded finished product of the housing A2. Particularly, the quality of a lens face A6 of the lens A5 of FIG. 1 has important influence on the quality of the finished product of the OSA A1. The rate of good yield of the OSA A1 is therefore low and the calibration or assembling of the OSA A1 is difficult that in turn increases the manufacturing cost of the OSA A1.        2. In a conventional method for measuring and examining the OSA A1, fiber coupling efficiency is generally based on to adjust the position of the functional element on the housing A2. In other words, the optical fiber 20 must be connected to the first aperture A3 before the functional element 30 is assembled to the housing A2. And then, a measuring instrument is used to adjust the position of the functional element 30 based on the fiber coupling efficiency. In this case, the size and position of a focal spot of a laser beam emitted from the functional element and passed through the lens A5 are adjusted according to a desired specification, and the focal spot is then coupled with an inner end of the optical fiber 20 that has already been connected to the first aperture A3, so that a finish product satisfying the required specification is obtained. Please refer to TIA/EIA-455-203 for specifications for launched power distribution measurement procedure for graded-index multi-mode fiber transmitters. Since the conventional adjustment and measurement operation adjusts the position of the functional element is based on the fiber coupling efficiency, it fails to optimize the fiber transmission bandwidth, and accordingly, could not provide effective and precise measurement to directly adversely affect the quality of the finished OSA A1.        3. The above-mentioned conventional measuring method for adjusting the position of the functional element based on the fiber coupling efficiency further includes many latent and variable factors that would affect the measurement result. For example, there is a specific tolerance for the quality of optical fibers, and the quality of the functional element is not always the same (for example, the emission power of the laser diode is not always constant and unchanged). All these factors would result in errors in the measurement of the quality of finished TOSA. For example, in the conventional measuring method, whether a finished product of OSA is qualified for use is completely decided according to the emission power of the functional element or the quality and specification of the optical fiber being used at the time of aligning the functional element. Therefore, a product may be qualified only in terms of the functional element or the optical fiber being used at the time of alignment of the functional element. In the event the initially qualified OSA product is used at a different time and/or a different place, for example, when the OSA is coupled with another optical fiber, a difference in error between the two optical fibers might result in a poor quality OSA. That is, the conventional measuring method fails to control the quality of the finished OSA to result in a low rate of good yield.        
A two-piece housing is developed in an attempt to overcome the drawbacks existed in the integrally formed one-piece housing A2. FIGS. 2 and 3 shows a first housing B1 and a second housing B2 that are assembled together to provide a complete housing for OSA. The first housing B1 is provided at an end with an aperture B3 for an optical fiber B4 (20) to assemble thereto, and the second housing B2 is provided at an end opposite to the aperture B3 with an aperture 35 for a functional element B6 (30) to assemble thereto.
However, an OSA having a two-piece housing would still encounter the problems described in the above paragraph Nos. 2 and 3.
It is therefore desirable to develop a method for measuring and assembling a transceiver optical sub-assembly to overcome the problems existed in the conventional method for the same purpose.